When he placed his advertisement in the Telegraph, he ran the risk of being dismissed as a fantasist.

The appeal was brief and to the point: "Fancy rafting across the Atlantic? Famous traveller requires 3 crew. Must be OAP. Serious adventurers only."

But it caught the eye of several experienced seafarers - and now 84-year-old Anthony Smith is preparing to lead his veteran team across the ocean in a vessel made from plastic gas pipes.

In a few months the team will push off their craft from the Canary Islands bound for a beach in the Bahamas, 2,800 miles away, on a voyage that would make most people, never mind octogenarians, quiver with fear.

Mr Smith, an adventurer, writer and grandfather, will be attempting to satisfy a lifelong itch to cross the ocean on one of the most primitive forms of transport.

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What makes the expedition even more extraordinary is that he will be setting off two years after he was run over by a van, an accident that left him with metal pins in his leg and walking with the help of a stick.

The former RAF pilot rejects the idea he is too old to embark on the 60-day crossing, and insists that rafting is relatively safe.

"Most people my age are happy with a trip to Sainsbury's every Tuesday, or maybe helping out fixing the church hall roof," he said. "What I want to show is that you don't have to be satisfied with a trip to the supermarket. You can do other things."

Mr Smith, a former science correspondent of The Daily Telegraph, has written over 30 books, worked on several film and documentary projects, and even presented Tomorrow's World when the BBC television show was in its infancy.

In his long adventuring career, he led a pioneering expedition over East Africa in 1962, The Sunday Telegraph Balloon Safari. The following year he became the first Briton to go over the Alps by hot air balloon.

He came up with the idea of rafting across the Atlantic in 1952, starting from the Canaries and sustaining himself with fish caught from the sea.

"I was a student then and I ran out of money. But the idea has always niggled me," he says.

The Telegraph advertisement, placed five years ago, caught the eye of David Hildred, a civil engineer and ocean yacht master.

As a schoolboy he had read Mr Smith's ballooning book Throw Out Two Hands and had become captivated by the adventurer's remarkable life.

"I'd always followed his career," said Mr Hildred, "and after seeing the advert I tracked Anthony down. We arranged a meeting and got on incredibly well - so much so he offered me a place on the raft.

"To be doing this with one of my childhood heroes is a dream come true."

At 57, Mr Hildred is not quite a pensioner but has already travelled widely, explored the Amazon in a dug-out canoe, and sailed the Atlantic.

Also on the raft will be experienced seaman Andy Bainbridge, 56, a close friend of Mr Hildred who keeps llamas and is currently studying alternative medicine in the wilds of Canada.

Robin Batchelor, 61, a professional balloonist whose adventures with actor Stephen Tompkinson are currently being screened on ITV, is considering completing the four-man crew.

Whilst he describes himself as "an airman, not a water baby", he admits to being "swept away" by Mr Smith's enthusiasm.

He said: "Anthony's so determined, he's completely dismissed the fact he got run over. Mentally he's as sharp as razor, he's completely occupied with the planning. There's no stopping him."

The team aims to launch in January, when the trade winds are at their strongest and before the Atlantic storms are most likely to hit.

The raft is being built from 13-yard (12-metre) sections of pipe donated by a manufacturer. Those at either end will be sealed full of air, providing buoyancy.

Those in the middle will contain drinking water and ballast. Crew members will live in two small shelters adapted from pig huts.

A fence will prevent the crew falling overboard, while Mr Smith will be constantly attached to a harness.

The men will manoeuvre the craft using small Peruvian-style rudders, known as guaras, which Mr Smith insists will provide greater flexibility than a conventional rudder.

A support vessel will accompany the raft for the first few days at sea, "in case we forget the can opener". A film of the voyage is planned, and Mr Smith hopes that schools will follow his progress.

The raft, called the An-tiki - adapted from the Kon-Tiki, the raft used by Norwegian explorer and writer Thor Heyerdahl in his 1947 expedition from South America to the Polynesian islands - will be easy to spot as it approaches land.

"We're going to put a giant 'elderly crossing' sign on the sail," said Mr Smith.